Abstract: A roller retainer for the third axis of a mouse comprises a seat, an upper cover and a roller seat. The seat has a housing, a circuit board and other components. The circuit board is installed with a microswitch and an IR module seat. A via hole is formed at the middle portion of the roller seat. The via hole serves to place a roller seat therein. A rear end of the roller seat is buckled to the rear inner end of the upper cover, and the roller seat may be like a suspending arm. The roller seat has a function of plastic resilient and therefore, no elastic spring is necessary. The roller seat is installed with an upper cover and other components is still installed in the seat. Therefore, no space in the circuit board is occupied and thus cost is reduced and material can be prepared easily.